When an AN polymer is heat-treated at high temperatures in the presence of a small amount of a non-solvent, the polymer and the non-solvent form a homogeneous fluid or melt, which exhibits fluidity like melts of polyesters and polyamides. Some methods for shaping the melt into fibers, etc. are known, for example, as proposed in U.S. Pat. No. 3,388,202, Japanese Patent Laid-Open Nos. 48-28982, 48-49839, 48-52832, etc. Many of these methods use water as the non-solvent for AN polymers and are characterized in that they give shaped articles of AN polymers without using any conventional expensive solvents such as dimethylsulfoxide, dimethylformamide, aqueous solutions of rhodanates, concentrated nitric acid, etc.
Methods of producing AN polymer melts at the same time of the polymerization of AN by applying the melting phenomenon of AN polymers to the polymerization system have been disclosed in Japanese Patent Laid-Open Nos. 50-97683, 54-30281, 54-23724, 54-93122, while Japanese Patent Laid-Open No. 51-101061 has proposed the use of AN monomer as the plasticizer for the polymers to enhance their plasticization. Given the situations, methods of using AN polymer melts for producing shaped articles such as shaped plastics, films, fibers, etc. have become considered to be favorable from the viewpoint of reducing and simplifying the production steps, reducing the production costs, saving energy, etc.
However, when the AN polymer melts as produced in accordance with the methods for producing them simultaneously with the polymerization of AN alone or a monomer mixture consisting essentially of AN (hereinafter referred to as "an AN monomer mixture"), such as those described in the above-mentioned patent publications, or in accordance with the method of using AN as the plasticizer that enhances the plasticization of AN polymers, such as that described in Japanese Patent Laid-Open No. 51-101061, are shaped into articles, the articles contain, immediately after the production thereof, the non-reacted monomer mixture consisting essentially of AN and even the AN monomer used as the plasticizer.
AN is toxic and must not be contained in final products. Therefore, AN must be completely removed prior to the final step of completing final products. For these reasons, the shaped AN polymer products are treated in water or hot water for many hours or are treated under reduced pressure, thereby removing AN therefrom. In addition, AN thus removed from the products must be completely recovered. Some equipment is required for the removal and recovery of AN, which, however, is problematic in that the producibility of the intended products is lowered and the costs for producing them are increased.